1. Field of the Invention
The present invention relates to a method for synthesizing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or its derivatives, particularly to a method using a single reaction vessel and does not require isolation of intermediates.
2. Description of the Prior Arts
9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, which may be referred to as ‘DOPO’, is a compound broadly used for antibacterial agents, antioxidants, fading resistant agents and fire retardants. The compound is not halide and thus can be used as a flame-retarding monomer without negative effects on the environment. Furthermore, the compound is used universally for synthetic fibers, plastic materials used for electronic devices, copper clad laminate on printed circuit boards, packaging materials for semiconductors, and photosensitive materials to increase flame-retardant capability of materials.
Since 1972, a method for synthesizing DOPO has been constantly researched and improved in patents such as U.S. Pat. Nos. 4,086,206, 5,391,798, 5,481,017, 5,650,530, 5,821,376, 6,107,506, EP 739896, EP0582957A1, DE 19505352, DE 19505353, CN 101108864A and in the journal Polymer, 39,5819-5826, 1998. The method for synthesizing DOPO comprises steps of: providing 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin; hydrolyzing 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin to form 2-(hydroxy-bipheny1-2-y1)-phosphinic acid by a hydrolytic process; and dehydrating 2-(hydroxy-bipheny1-2-y1)-phosphinic acid to form DOPO at high temperature under vacuum to remove water.
The hydrolytic processes can be classified as basic, solvent, direct, ice or alcohol hydrolysis, and are described below.
A. basic hydrolysis: 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin is put into a basic solution and to which is added hydrogen sulfate to form 2-(hydroxy-biphenyl-2-yl)-phosphinic acid that is incubated at high temperature under 90 Kpa to form DOPO.
B. solvent hydrolysis: 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin is added to an organic solvent for hydrolysis and crystallization and incubated at high temperature under vacuum to form DOPO .
C. direct hydrolysis: 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin is added to equal moles of deionized water at a temperature between 80 and 130° C. for 3 to 10 hours for hydrolysis and incubated at high temperature under vacuum to form DOPO.
D. ice hydrolysis: 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin is added over ice to be hydrolyzed to form 2-hydroxy-bipheny1-2-y1)-phosphinic acid that is then dehydrated to form DOPO.
E. alcohol hydrolysis: 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin is added to a molar equivalent of deionized water and an appropriate amount of alcohol to facilitate contact between 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin and water, to accelerate the hydrolytic process and form 2-(hydroxy-biphenyl-2-yl)-phosphinic acid that is incubated at high temperature under vacuum to form DOPO.
However, the above-mentioned hydrolytic processes have great drawbacks for the following reasons:
(1) Reaction times of the hydrolytic processes are too long.
(2) Each hydrolytic process requires purification of intermediates and further dehydration and cyclization reaction to form final product. Therefore, the processes are complicated.
(3) For some of the processes, highly-polar organic solvents are required to manufacture and purify products. Therefore, said processes easily cause environmental pollution.
(4) Since each process requires use of great quantities of deionized water, a lot of waste, which pollutes the environment, is generated.
(5) Since each process requires separation of intermediates, yields are low.
(6) Each process has multiple purifying steps to manufacture DOPO, so purity and color of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are not easy to be controlled.
(7) The processes are complicated, so manufacturing costs of product are high.
(8) Each process consumes much energy.
To overcome the shortcomings, the present invention provides a method for synthesizing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or a derivative thereof to mitigate or obviate the aforementioned problems.